The present invention relates to a steam generator having an improved structural support system and an improved combined hot solids-gas separator for separating gas and solids from a combined gas-solids stream and, more particularly, to a circulating fluidized bed steam generator (CFB) having an improved structural support system and an improved combined hot solids-gas separator.
Steam generators including circulating fluidized bed steam generators can achieve a substantial size requiring commensurately substantial structural support systems. U.S. Pat. No. 4,286,549 to Eisinger illustrates one variation of a common structural support system known as a top support system in which the steam and heat cycle components are suspended from a structural support frame which permits thermal expansion of these components during their operation. Such structural support frames include vertical post members disposed adjacent front, rear, and sides of the overall configuration of the steam and heat cycle components and a plurality of laterally extending members above this overall configuration. A plurality of tie rods mounted to the laterally extending members extend vertically to connect to the steam and heat cycle components so as to thereby suspend these components from the laterally extending members of the structural support system.
U.S. Pat. No. 4,745,884 to Coulthard discusses some of the drawbacks associated with top support systems due to, among other reasons, the separation and spaced-apart location of the various components. Also, the impact of the use of refractory materials is noted therein including the impact on the weights of the components and the impacts on maintenance procedures and schedules for completing and maintaining an operative system. These various impacts make it generally desirable to minimize the amount of refractory material used. Another drawback noted in the Coulthard reference is the differential thermal movements between component parts which engender commensurate reinforcement of the structural support system--with attendant weight and material cost increases of the support system. Accordingly, the need exists for a steam generator whose individual components can be relatively closely positioned to one another while minimizing the demands placed upon the structural support system which supports the individual components relative to one another.
Additionally, steam generators such as circulating fluidized bed steam generators typically employ mechanical separators for separating from one another two constituent elements of the flue gas produced by the combustion process--namely, hot solids and gas. One type of separator for separating solids and gases in a combined solids-gas stream has been characterized as a cyclone separator due to the fact that it typically comprises a vertical cylindrical separation chamber having a lower end of diminishing horizontal cross-section. Typically, hot flue gases which have exited a furnace volume of a solids recirculating type of fossil fuel-fired system are flowed into the upper region of the cyclone separator. In the cyclone separator, the different influences of centrifugal force on the solids in comparison with the gases are capitalized upon to create a downward movement of the solids while the gases are drawn into a swirl or vortex movement. Ultimately, a relatively large fraction of the solids move downwardly into a discharge or collections region at the base of the cyclone separator.
Cyclone separators have been designed with a gas outlet duct extending downwardly through a top wall of the separation chamber to a location at which the gases moving in the vortex now enter the gas outlet duct and exit the cyclone separator. Cyclone separators have also been proposed with a gas outlet duct extending upwardly through a bottom wall of the separation chamber. For example, U.S. Pat. No. 4,874,584 to Ruottu discloses a cyclone separator in which the gases flowing tangentially from the upper part of a fluidized bed reactor are discharged through a discharge pipe going through the bottom of the vortex chamber.
The Ruottu patent discloses that its cyclone separator arrangement provides some advantages over conventional cyclone separator arrangements such as, for example, the advantage that the axial and radial velocities prevailing in the lower part of its disclosed flow-through reactor are low, but the tangential velocity is high. Thus, according to the Ruottu patent, dust entrained by an eventual suction flow cannot get into the discharge pipe but is separated onto the walls and returned to the fluidized bed reactor.
Notwithstanding the alleged advantages of a cyclone separator arrangement having a downwardly exiting gas discharge pipe, there has been an unmet need for proposals of an arrangement which might capture these advantages without disproportionately sacrificing the advantages provided by the conventional top exiting gas discharge pipe arrangements. For example, it would be a beneficial contribution to the cyclone separator art if an arrangement were to be provided which maintains or even increases the separation efficiency of the separator while improving up to optimizing the vortex flow of the gases in the separator.